The use of security features that are printed in a wavy pattern or wave shape on a security document are known from EP 2 035 236 B1 and U.S. Pat. No. 6,164,701. These security features generally comprise a string of alphanumeric characters derived from personal data, for example the date of birth and/or the name, of the intended holder of the security document.
An example of a warped security feature 2 is illustrated in FIG. 1. To produce the security feature 2 on the security document, the characters that are intended to form the security feature 2 are entered and processed to produce a bitmap image. The characters are transformed along a given arc, curve or warped into a hull which generally involves warping a “straight” object such as the characters by a given mathematical transformation. The bitmap image is then sent to a laser processing mechanism or inkjet printer to print the security feature 2 like any conventional text or image bitmap image. The security feature 2 is formed by a series of small spots 4 on the security document based on the bitmap image. The security feature 2 is printed line-by-line 6 in a vertical direction, with the spots 4 that form the characters of the security feature being generally evenly spaced according to the generated bitmap pattern.
However, any counterfeiter that is capable of preparing an image containing an image or text warped to a given curve can take any regular laser processing equipment or printing equipment and fake the security feature 2. Therefore, since the output of the conventional warped security feature is a bitmap image which can be printed using conventional printing technology, the security afforded by the security feature 2 resides primarily in the data generation process.
Pure vector mode is available on some laser processing devices. Vector mode is typically used as a fast way to laser mark text or simple logos. Most laser processing devices use a mirror system to deflect the laser light to the final position. In vector mode, those mirrors are programmed (controlled) to follow a vectorial description of a text or image to be produced, most often defined by a series of short straight lines, sometimes arches, Beziér splines or a series of single finite positions.
In pure bitmap mode or image mode, the laser light scans the target area in straight lines (typically horizontal or vertical) and while the area is scanned, producing laser pulses. The result is a rectangular matrix in which single dots are either “set” (laser fired) or “not set” (laser not fired). On grayscaling laser processing devices, the power of single laser dots might differ to produce darker or lighter dots.
As this technique is very similar to what laser printer equipment or inkjet printers do when it comes to creating (rasterizing) images, except for the fact that laser processing is based on a reaction in the target material rather than to applying ink or toner to an object, the results look very similar.
Improvements to the production of warped security features are needed to prevent fraud using widely available home/office accessible reproduction devices.